inventory left-click does not work with TS mode off, it only works when it is on. however, when touchscreen mode is on, shift-clicking does not work. also, shift double clicking just doesn't work either way.
TS On: left click works, not shift-clicking, can't drag stacks to distribute them into slots, occasionally will not allow me to drag and combine stacks
TS Off: left click does not work, shift-clicking does
[I've also made this post before but forgot I left optifine on, since then I've confirmed this issue is also present in vanilla for me]